1. Field of the Invention
This invention relates to improved techniques for utilizing magnetic bubble domains, and more particularly to novel techniques for moving and discriminating between different types of these bubble domains using in-plane magnetic fields which are time varying and spatially uniform. Bubble domains are moved in a magnetic medium without the need for spatial magnetic gradients acting on the bubbles.
2. Description of the Prior Art
In the bubble domain art, many techniques are known for moving magnetic bubble domains. These techniques generally require the presence of active overlays, such as conductor overlays and magnetic element overlays. Thus, either by application of current to conductor overlays, or by application of reorienting in-plane magnetic fields, bubble domains can be made to follow prescribed paths in the bubble domain medium. Still another type of bubble domain propagation utilizes modulations of the bias field in combination with wedge-shaped patterns of magnetic material. The bubble domain is made to expand and contract and will thereby be moved along from one triangular wedge to the next due to the asymmetry of wall motion produced by the triangular wedges. In all these types of bubble propagation schemes, some type of overlay structure is generally used to provide the forces which move the bubbles.
In copending application Ser. No. 659,880, filed Feb. 20, 1976, and assigned to the present assignee, a new type of bubble domain propagation, termed automotion, is described which utilizes time varying magnetic fields which are spatially uniform. As an example, a time varying magnetic field directed along the cylinder axis of the bubble domain is applied in order to change (precess) the wall magnetization vector distribution along the bubble domain wall. This in turn provides a reaction force which moves the bubble domains in a desired direction. In order to have continuous bubble motion in response to the time varying magnetic field, the original state of the domain wall magnetization vectors is generally restored by a D.C. magnetic field prior to each application of the time varying magnetic field. This type of bubble domain motion does not require active overlay structures and has several advantages, as are pointed out in that copending application.
Another copending application, Ser. No. 697,170, filed June 17, 1976 and now U.S. Pat. No. 4,068,220, describes how to selectively and controllably convert one wall magnetization distribution of a bubble to a different wall magnetization distribution and how to use the principles of bubble automotion to sense the resulting wall state. In particular, techniques are shown for applying magnetic fields to bubble domains having winding number S=1 for conversion to a new configuration bubble which still has winding number S=1. As will be appreciated by those of skill in the art, the winding number S, or revolution number, is the number of rotations the wall moment at a point P makes when P goes once around the periphery of the domain wall. This concept is described in more detail in U.S. Pat. No. 3,890.605, assigned to the present assignee, and in an article by J. C. Slonczewski et al, 18th Annual Conference on Magnetism and Magnetic Materials, Denver, Colo., which appeared in the AIP Conference Proceedings 10, p. 458 (Nov. 28-Dec. 1, 1972).
The concept of bubble domain automotion using gradientless magnetic fields, described in the aforementioned copending applications, has also been described in an article entitled "Gradientless Propulsion of Magnetic Bubble Domains", by B. E. Argyle et al, which appeared in the Journal of Magnetism and Magnetic Materials, Volume 2, No. 4, July/August 1976, at pp. 357-360. In addition, reference is made to an invited paper by B. E. Argyle et al, entitled "Gradientless Propulsion of Bubble Domains" presented as Paper 7A-1 at the Joint MMM-Intermag Conference, June 15-18, 1976, at Pittsburgh, Pa. The text of this presentation is in AIP Conference Proceedings No. 34, p. 131, 1976.
Whereas the previously described techniques for bubble automotion have been demonstrated using time varying magnetic fields directed along the easy axis of magnetization of the magnetic bubble film, the present invention utilizes time varying magnetic fields which are in the plane of the magnetic bubble domain medium. These time varying, in-plane magnetic fields are spatially uniform and act directly on the magnetization vectors in the bubble wall to produce a direct bubble translation by action on these vectors. This is in contrast with the previously described type of bubble automotion in which the translation is secondary to a change in radius of the bubble domains occurring when they are subjected to time varying magnetic fields directed along the bubble domain axis. Thus, while the previously described bubble domain automotion and the present technique for bubble automotion both apply spatially invariant, time varying magnetic fields to the bubble domains in order to effect their wall magnetization distribution, the present invention differentiates from that previous automotion technique (termed type I automotion) in several ways.
In the present type of automotion, the bubble domain center can displace by a greater amount per applied magnetic field pulse than was the case for type I automotion. The control of velocity afforded by the direct action of the in-plane field on the Bloch lines, rather than indirect action through a radius change, leads to easy optimization of the mean velocity. Further, in this second type of automotion, termed Automotion Type II, the bubble domain is less likely to undergo a state change when being automoted. Field coils similar to those used for T-I bar structures can be utilized. For a given bubble diameter, the optimum data rate is comparable to that of T and I-bar devices. Since in-plane fields are used, bias field margins in the bubble chip are not adversely affected. Even when the magnetic bubble domains have small diameters, the magnetic field strengths of the time-varying field are comparable to those used in T and I bar devices. Another desirable feature of type II automotion is that a multiplicity of automotion directions is available merely by changing the signs of the in-plane fields used to translate the bubbles. These advantages and features will become more apparent in the detailed description of the preferred embodiments.
Accordingly, it is a primary object of the present invention to produce bubble domain automotion using a direct coupling of the applied magnetic fields to the wall magnetization vectors in the periphery of the domain wall.
It is another object of the present invention to utilize time varying, spatially uniform magnetic fields in the plane of the bubble domain medium for moving bubble domains.
A further object of the present invention is to provide bubble domain propagation using in-plane magnetic fields, by a technique which is not lithography-limited.
A still further object of the present invention is to provide additional techniques for discriminating magnetic bubble domains which have differing wall structures and the same, or different, winding numbers.
A further object of this invention is to provide bubble domain propagation of very small bubble domains, using magnetic drive fields whose amplitudes are readily attainable.